There are a number of assemblies that utilize actuators, such as those presently found in and used in the opening and closing of an object, such as a door or enclosure mechanisms. According to one example, requirements dictate that the hand force required to close a pivot type stowage bin on a commercial aircraft can be no more than 25 lbs when the stowage bin is loaded with luggage. As a result, there is a general need in the field to provide a device that can provide a sufficient lift assist force when needed, therefore decreasing the hand force that is required to close the stowage bin.
According to another example, an actuator is required to provide assistance in the opening of an aircraft engine cowl. Due to the location of the typical mounting points of the actuator, the actuator length must shorten (i.e., compress) upon initial opening of the cowl. As the cowl rotates, the actuator reaches a point where its axis is in line with the pivot point (e.g. an over center condition), and the actuator is at its minimum length. As the cowl continues to rotate and pass the over center condition, the actuator extends over the remainder of the cowl rotation until the cowl reaches the open position. It is desired that the actuator does not impede the opening of the engine fan cowl during the initial opening before the over center condition and provide an assisting extension force after passing the over center condition.
The problem for the foregoing is in providing a spring actuator that compresses freely for the initial opening of the cowl. As the actuator passes the over center condition, the actuator should provide a spring extension force as the actuator extends to aid in opening the engine fan cowl for the remainder of the rotation. When closing the cowl, the actuator must provide a resisting extension force as the actuator compresses until the actuator again passes the over center condition, then capture the spring force so that the unit extends freely for the remainder of the cowl closing rotation.